1. Field of the Invention
The present invention relates to a scanning probe microscope.
2. Description of the Related Art
A scanning probe microscope (SPM) is a generic name of a scanning microscope in which scanning is performed with a mechanical probe to acquire information of the surface of a sample, whereby mapping display is done. The SPMs include a scanning tunneling microscope (STM), an atomic force microscope (AFM), a scanning magnetic force microscope (MFM), a scanning near field optical microscopy (SNOM), and the like.
Among the SPMs, the AFM is used most extensively, and comprises, as main elements, a cantilever having a mechanical probe at its free end, an optical displacement sensor to detect a displacement of the cantilever, and a scanning mechanism in which a mechanical probe and a sample are relatively scanned. As the optical displacement sensor, an optical lever type optical displacement sensor is used most extensively, because of simple constitution and nevertheless high detection sensitivity. In this optical lever type optical displacement sensor, a light beam having a diameter of several μm to several tens μm is applied onto the cantilever, and a change in a reflection direction of reflected light corresponding to a change of a warp of the cantilever is caught by a two-divided optical detector or the like, to output an electronic signal in response to a behavior of the mechanical probe at the free end of the cantilever. According to the AFM, relative positions of the mechanical probe and the sample are scanned in XY directions by the scanning mechanism, while a relative distance between the mechanical probe and the sample is controlled in a Z direction so that the output of the optical displacement sensor is constant, whereby a rough state on the surface of the sample is brought into mapping and displayed on a monitor of a computer.
In the AFM, a mode (an AC mode) is often employed wherein the cantilever is vibrated, and on the basis of the resultant vibration properties, an interaction caused between the sample and the probe is inspected. This is for an advantage of the AC mode that a power caused between the sample and the probe can be kept more weakly as compared with a usual mode, (which is called a contact mode). In this AC mode AFM, the vibration of the cantilever caused by the interaction between the sample and the probe, i.e., one of an amplitude change and a phase change of a displacement is detected, and on the basis of the detected results, a surface shape of the sample is determined.
Jpn. Pat. Appln. KOKAI Publication No. 2008-232984 discloses one of this type of AC mode AFMs. This AC mode AFM is constituted to switch one of an amplitude change and a phase change, followed by detection.